Creating a Custom Properties Tab in Blender 2.80
The code you've posted adds a tab to the Tool Shelf, not the Properties. As far as I know you cannot add new tabs to the properties, you can however add tabs in the 3D View.



In Blender 2.8 you need the following attributes to create your own tab:

bl_category = "Name of your tab"
bl_space_type = "VIEW_3D"
bl_region_type = "UI"


A minimal add-on that adds a panel in a separate tab:

import bpy

class EXAMPLE_PT_panel(bpy.types.Panel):
    bl_label = "My own addon"
    bl_category = "Name of your tab"
    bl_space_type = "VIEW_3D"
    bl_region_type = "UI"

    def draw(self, context):
        layout = self.layout

        layout.label(text="This is a label")


classes = (EXAMPLE_PT_panel,)


def register():
    for cls in classes:
        bpy.utils.register_class(cls)


def unregister():
    for cls in classes:
        bpy.utils.unregister_class(cls)

if __name__ == "__main__":
    register()